Gas delivery devices such as mass flow meters (MFMs) and mass flow controllers (MFCs) are important components of accurately delivering process gasses to, for example, semiconductor manufacturing. Both the shrinking size of semiconductor devices and the need to reduce the capital equipment cost in semiconductor device fabrication is driving the need for gas flows to be accurately delivered over a wider and wider range of gas flows.
Currently the need for accuracy at both low flows and higher flow on the same process gas can require two separate gas delivery lines—one gas line for lower mass flow rates and one gas line for higher mass flow rates. The conventional dynamic accuracy range of 1% of reading accuracy for a thermal MFC is roughly less 5 to 1 (20% to 100% of full scale). Alternatively, gas delivery is slowed down so that a thermal MFC can operate within its low mass flow accuracy range.
Therefore, what is needed is a technique in gas delivery systems to overcome the shortcomings of the prior art by markedly increasing the dynamic range of an MFM or MFC where the device provides the needed accuracy, and reducing the number of devices necessary for gas delivery.